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  <title>Blockly Demo: Step Execution with JS Interpreter</title>
  <script src="acorn_interpreter.js"></script>
  <script src="../../blockly_compressed.js"></script>
  <script src="../../blocks_compressed.js"></script>
  <script src="../../javascript_compressed.js"></script>
  <script src="../../msg/js/en.js"></script>
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    h1 {
      font-weight: normal;
      font-size: 140%;
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  <h1><a href="https://developers.google.com/blockly/">Blockly</a> &gt;
    <a href="../index.html">Demos</a> &gt; Step Execution with JS Interpreter</h1>

  <p>This is a demo of executing code step-by-step with a sandboxed JavaScript interpreter.</p>

  <p>The generator's <code>Blockly.JavaScript.STATEMENT_PREFIX</code> is assigned <code>'highlightBlock(%1);\n'</code>,
  where <code>%1</code> is the block id. The call to <code>highlightBlock()</code> will highlight the identified block
  and set the variable <code>highlightPause</code> to <code>true</code>.</p>

  <p>"Parse JavaScript" will generate the code and load it into the interpreter. Then, each press of the
  "Step JavaScript" button will run the interpreter one step until the <code>highlightPause</code> is true.
  That is, until <code>highlightBlock()</code> has highlighted the block that will be executed on the next step.</p>

  <p>&rarr; <a href="https://developers.google.com/blockly/guides/configure-blockly/web/running-javascript#js_interpreter">More info on running code with JS Interpreter</a></p>

  <p>
    <button onclick="stepCode()" id="stepButton">Step JavaScript</button>
  </p>

  <div style="width: 100%">
    <div id="blocklyDiv"
        style="display: inline-block; height: 480px; width: 58%"></div>
    <textarea id="output" disabled="disabled"
        style="display: inline-block; height: 480px; width: 38%;">
    </textarea>
  </div>

  <xml xmlns="https://developers.google.com/blockly/xml" id="toolbox" style="display: none">
    <category name="Logic" colour="%{BKY_LOGIC_HUE}">
      <block type="controls_if"></block>
      <block type="logic_compare"></block>
      <block type="logic_operation"></block>
      <block type="logic_negate"></block>
      <block type="logic_boolean"></block>
    </category>
    <category name="Loops" colour="%{BKY_LOOPS_HUE}">
      <block type="controls_repeat_ext">
        <value name="TIMES">
          <block type="math_number">
            <field name="NUM">10</field>
          </block>
        </value>
      </block>
      <block type="controls_whileUntil"></block>
    </category>
    <category name="Math" colour="%{BKY_MATH_HUE}">
      <block type="math_number">
        <field name="NUM">123</field>
      </block>
      <block type="math_arithmetic"></block>
      <block type="math_single"></block>
    </category>
    <category name="Text" colour="%{BKY_TEXTS_HUE}">
      <block type="text"></block>
      <block type="text_length"></block>
      <block type="text_print"></block>
      <block type="text_prompt_ext">
        <value name="TEXT">
          <block type="text"></block>
        </value>
      </block>
    </category>
    <sep></sep>
    <category name="Variables" custom="VARIABLE" colour="%{BKY_VARIABLES_HUE}">
    </category>
    <category name="Functions" custom="PROCEDURE" colour="%{BKY_PROCEDURES_HUE}">
    </category>
  </xml>

  <xml xmlns="https://developers.google.com/blockly/xml" id="startBlocks" style="display: none">
    <block type="variables_set" id="set_n_initial" inline="true" x="20" y="20">
      <field name="VAR">n</field>
      <value name="VALUE">
        <block type="math_number">
          <field name="NUM">1</field>
        </block>
      </value>
      <next>
        <block type="controls_repeat_ext" id="repeat" inline="true">
          <value name="TIMES">
            <block type="math_number">
              <field name="NUM">4</field>
            </block>
          </value>
          <statement name="DO">
            <block type="variables_set" id="set_n_update" inline="true">
              <field name="VAR">n</field>
              <value name="VALUE">
                <block type="math_arithmetic" inline="true">
                  <field name="OP">MULTIPLY</field>
                  <value name="A">
                    <block type="variables_get">
                      <field name="VAR">n</field>
                    </block>
                  </value>
                  <value name="B">
                    <block type="math_number">
                      <field name="NUM">2</field>
                    </block>
                  </value>
                </block>
              </value>
              <next>
                <block type="text_print" id="print">
                  <value name="TEXT">
                    <block type="variables_get">
                      <field name="VAR">n</field>
                    </block>
                  </value>
                </block>
              </next>
            </block>
          </statement>
        </block>
      </next>
    </block>
  </xml>

  <script>
    var demoWorkspace = Blockly.inject('blocklyDiv',
        {media: '../../media/',
         toolbox: document.getElementById('toolbox')});
    Blockly.Xml.domToWorkspace(document.getElementById('startBlocks'),
                               demoWorkspace);

    var outputArea = document.getElementById('output');
    var stepButton = document.getElementById('stepButton');
    var myInterpreter = null;

    function initApi(interpreter, globalObject) {
      // Add an API function for the alert() block, generated for "text_print" blocks.
      interpreter.setProperty(globalObject, 'alert',
          interpreter.createNativeFunction(function(text) {
        text = arguments.length ? text : '';
        outputArea.value += '\n' + text;
      }));

      // Add an API function for the prompt() block.
      var wrapper = function(text) {
        return interpreter.createPrimitive(prompt(text));
      };
      interpreter.setProperty(globalObject, 'prompt',
          interpreter.createNativeFunction(wrapper));

      // Add an API function for highlighting blocks.
      var wrapper = function(id) {
        id = String(id || '');
        return interpreter.createPrimitive(highlightBlock(id));
      };
      interpreter.setProperty(globalObject, 'highlightBlock',
          interpreter.createNativeFunction(wrapper));
    }

    var highlightPause = false;
    var latestCode = '';

    function highlightBlock(id) {
      demoWorkspace.highlightBlock(id);
      highlightPause = true;
    }

    function resetStepUi(clearOutput) {
      demoWorkspace.highlightBlock(null);
      highlightPause = false;

      if (clearOutput) {
        outputArea.value = 'Program output:\n=================';
      }
    }

    function generateCodeAndLoadIntoInterpreter() {
      // Generate JavaScript code and parse it.
      Blockly.JavaScript.STATEMENT_PREFIX = 'highlightBlock(%1);\n';
      Blockly.JavaScript.addReservedWords('highlightBlock');
      latestCode = Blockly.JavaScript.workspaceToCode(demoWorkspace);
      resetStepUi(true);
    }

    function stepCode() {
      if (!myInterpreter) {
        // First statement of this code.
        // Clear the program output.
        resetStepUi(true);
        myInterpreter = new Interpreter(latestCode, initApi);

        // And then show generated code in an alert.
        // In a timeout to allow the outputArea.value to reset first.
        setTimeout(function() {
          alert('Ready to execute the following code\n' +
            '===================================\n' + latestCode);
          highlightPause = true;
          stepCode();
        }, 1);
        return;
      }
      highlightPause = false;
      do {
        try {
          var hasMoreCode = myInterpreter.step();
        } finally {
          if (!hasMoreCode) {
            // Program complete, no more code to execute.
            outputArea.value += '\n\n<< Program complete >>';

            myInterpreter = null;
            resetStepUi(false);

            // Cool down, to discourage accidentally restarting the program.
            stepButton.disabled = 'disabled';
            setTimeout(function() {
              stepButton.disabled = '';
            }, 2000);

            return;
          }
        }
        // Keep executing until a highlight statement is reached,
        // or the code completes or errors.
      } while (hasMoreCode && !highlightPause);
    }

    // Load the interpreter now, and upon future changes.
    generateCodeAndLoadIntoInterpreter();
    demoWorkspace.addChangeListener(function(event) {
      if (!(event instanceof Blockly.Events.Ui)) {
        // Something changed. Parser needs to be reloaded.
        generateCodeAndLoadIntoInterpreter();
      }
    });
  </script>
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